1. Field of the Invention
This invention relates to a variable capacity vane compressor which is capable of varying the delivery quantity or capacity of the compressor.
2. Description of the Prior Art
A conventional variable capacity compressor has been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 63-259190, which includes a hollow cylinder formed within a housing, a rotor rotatably received within the hollow cylinder, a pair of side blocks fixed to respective opposite ends of the cylinder for closing same, and a plurality of vanes slidably fitted within respective slits formed in the rotor for dividing the space formed between the inner peripheral surface of the hollow cylinder and the outer peripheral surface of the rotor into a plurality of compression chambers, each of the plurality of compression chambers being caused to communicate with alternate ones of an inlet port and an outlet port, for drawing a refrigerant gas therein, compressing the refrigerant gas, and discharging the compressed refrigerant gas therefrom. The vane compressor has a rotation plate rotatably arranged between one of the pair of side blocks, i.e. a front side block, and the rotor, for controlling the maximum capacity of each compression chamber when it is shut off from the outside, and a spool slidably received within a spool-receiving chamber formed in the front side block, the spool having a pin of the rotation plate engaged therein, with the spool-receiving chamber being divided by the spool into a first pressure chamber into which is introduced the refrigerant gas at pressure corresponding to delivery pressure and a second pressure chamber into which is introduced an oil at pressure corresponding to delivery pressure via a valve mechanism which utilizes suction pressure, whereby as a result of the conflict between the pressures in the first and second pressure chambers, the rotation plate is driven for rotation. On the other hand, a sealing portion is provided between the rotation plate and the front side block for separation of upper and lower pressure regions from each other, while a supply passage is provided for communication with the sealing portion to supply an oil at pressure corresponding to the delivery pressure to the sealing portion.
In general, in the variable capacity vane compressor of this kind, when the gap between the rotation plate and the cylinder becomes large, the amount of blow-by gas leaking from the compression chambers in the hollow cylinder via the gap increases to lower compression efficiency (volume efficiency .eta.v), the vane back pressure acting on the vanes decreases to cause chattering of vanes, and/or noise is produced through play of the rotation plate. Therefore, it is required to press the rotation plate against the cylinder.
In the proposed variable capacity vane compressor, to prevent leakage of the refrigerant gas introduced into the first pressure chamber, which is at pressure corresponding to the delivery pressure, the sealing portion (an annular groove and a seal ring fit therein) is provided between the rotation plate and the front side block for sealed separation or shutting-off of the upper-pressure and lower-pressure regions from each other, and is supplied with a lubricating oil at pressure corresponding to the delivery pressure. As a result, the lubricating oil exerts high pressure corresponding to the delivery pressure directly on the rotation plate to press same against the cylinder side.
However, to sufficiently prevent leakage of the refrigerant gas introduced into the first pressure chamber, which is at pressure corresponding to the delivery pressure, with aid of the seal ring and the lubricating oil, it is required to press the seal ring against the rotation plate to such an extent as will prevent the lubricating oil from leaking between the seal ring and the rotation plate. Accordingly, the frictional force occurring between the seal ring and the rotation plate offers a large resistance against the rotation of the rotation plate, thereby preventing smooth rotation of the rotation plate.